This study will contrast two experimental treatment conditions by testing whether joint attention/joint engagement intervention using spoken communication (JAE-EMT) results in better outcomes than joint attention/joint engagement intervention that is instead supplemented with an individualized AAC system (JAE-AAC). Thus, the skills of joint attention/joint engagement (JAE) remain foundational to developing expressive language but the difference in the two treatments will be between whether the JAE is administered through the more traditional spoken means (EMT) or through an augmentative and alternative communication device (AAC).